The present invention relates generally to seals, and more particularly to a brush seal segment.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Annular brush seals have been proposed for use between a rotor and a surrounding casing in gas and steam turbines. The annular brush seal is made up of circumferentially-arrayed brush seal segments. Each brush seal segment is attached to the casing and includes a back (i.e., downstream) plate, a front (i.e., upstream) plate, and bristles which are positioned between the back and front plates with the free end of generally each bristle extending beyond the edges of the back and front plates. The bristles typically are canted at an angle of generally forty-five degrees in the direction of rotation of the rotor, and the free ends of the bristles are close to (and may even touch) the rotor. Typically, the front plate (and in some designs also portions of the back plate), near the free ends of the bristles, is spaced apart from the bristles to allow room for the bristles to flex and recover during transient encounters of the free ends of the bristles with the rotor. When the upstream gas flow is turbulent, some of the flow can swirl between the front plate and the bristles causing bristle flutter (i.e., instability) which quickly wears the bristles leading to premature brush seal failure. What is needed is a design for a brush seal segment which reduces bristle flutter in a turbulent-flow environment.